The present invention relates to an optical pickup device which has a plurality of light sources for outputting light of different wavelengths to optically record and replay information on disc-shaped recording media having different specifications.
As an optical disc from which signals are optically read using a light beam such as a laser beam, a compact disc (CD) has become widespread. In response to the need for a capacity larger than a CD, a high density disc (digital versatile disc (DVD)) which has been standardized for the purpose of achieving a larger capacity by enabling a recording density higher than a CD in addition to having the same diameter as a CD to keep mechanical compatibility, and a Blue-ray disc (BD) and a high definition (HD)-DVD for which a blue laser is used with the aim of a recording density higher than a DVD have been proposed. Signals recorded on such a high density disc are read by an optical pickup device having an optical system the resolution of which is made high using a semiconductor laser of a wavelength shorter than a normal wavelength.
By the way, there is a following method of allowing an optical pickup device to read signals on both of a CD and a high density disc. That is, an optical pickup device having three kinds of light sources of different wavelengths which are a laser diode for emitting a light beam suitable for a normal density recording medium, a laser diode for emitting a light beam suitable for a high density recording medium, and a laser diode for emitting a light beam suitable for a higher density recording medium are provided, and the light sources are switched according to the recording density of a recording medium from which signals are read, and thus signals on three kinds of recording media having different recording densities are read by this single optical pickup device (see, for example, JP 2001-256667A and JP 2003-203378A).
FIG. 25 shows an example of a conventional pickup device. This optical pickup device having three kinds of light sources for CD/DVD/BD use is provided with optical components, photodetectors, and signal detecting methods corresponding to the wavelengths of the light sources, to say nothing of the three kinds of light sources. In FIG. 25, the reference numeral 1 denotes a light source for BD use, 2 denotes a light source for CD use, 3 denotes a light source for DVD use, 4 denotes a beam splitter (BS) for splitting a light beam for BD use, 5 denotes a BS for splitting a light beam for CD use, 6 denotes a BS for splitting a light beam for DVD use, 7 denotes a collimating lens for CD/DVD use, 8 denotes a prism for BD use, 9 denotes a special collimating lens for BD use capable of correcting spherical aberration, and 10 denotes a prism for synthesis. Furthermore, a light receiving system 11 to 14 for CD/DVD use and a light receiving system 15 to 18 for BD use are disposed separately. The reference numeral 19 denotes an erecting mirror for erecting a light beam toward a disc (not shown).
Other optical pickup devices include an optical pickup device in which two optical pickups which are a first optical pickup corresponding to two wavelengths for CD and DVD use and a second optical pickup corresponding to a wavelength for BD use are mounted on a drive unit.
The aforementioned conventional optical pickup devices for CD/DVD/BD use have the following problems.
That is, there is a problem that the optical pickup device having the three kinds of light sources is required to be provided with optical components, photodetectors, and signal detecting methods corresponding to the wavelengths of the light sources, to say nothing of the three kinds of light sources, so that the optical system and circuit of the optical pickup device become complicated, thereby causing increase in cost and deterioration in reliability.
Furthermore, the optical pickup device in which the first optical pickup for CD/DVD use and the second optical pickup for BD use are mounted on the drive unit also has a problem that the cost and the device size increase because of the two optical pickups.